There are more indicators that suggest the growth is for real.
Compared to the third quarter, a more recent benchmark, the economy expanded by a very rapid 3.6%. And the government said Monday that full-year GDP growth in 2012 was 6.4%.
The massive floods in 2011 killed hundreds of people and caused damage worth billions of dollars. The country is a regional manufacturing hub, and is especially important for the auto and electronics sectors.
HSBC's Lim said the country's central bank is now less likely to cut rates later this week -- a strategy that some government officials have advocated in a bid to boost the economy.
"With growth this strong, it is difficult to make a case for more policy accommodation, no matter what the government may say about the need to compress interest rate differentials and keep [the baht] from strengthening," Lim said.
Rate cut or no, Thailand is projected to keep its momentum. The government forecasts growth of 4.5% to 5.5% for 2013, a number in line with private forecasts.